Microsatellite  instability (MSI) has been found in most hereditary nonpolyposis colorectal cancer HNPCC tumors and in a significantly smaller proportion of sporadic colorectal cancers (CRC). The primary aim of this study was the establishment of an effective assay for MSI detection in our laboratory. The secondary aim was the evaluation of MSI frequency in tumors of CRC patients from the Republic of Macedonia, and the comparison of MSI status with the histopathological features and clinical course of the disease. The fluorescent multiplex polymerase chain reaction (PCR) was found to be the method of choice for routine MSI analyses due to its simplicity, speed and lesser manipulation requirements. Of the five microsatellite markers used in this study, the BAT26 exhibited 100% sensitivity and 100% specificity in the detection of MSI-high phenotype in tumors and could be used as a single marker in MSI analysis. Fourteen of 107 (13.1%) tumors were MSI positive, 11 of which were classified as MSI-H (instability in three or more markers) and three as MSI-L (instability in only one marker). Nodal infiltration was absent in all patients with MSI tumors (p = 0.008).

Statistically significant association was also found with proximal localization (p <0.0001), Dukes' A and B stage of the tumors (p = 0.02) and mucionous histotype (p = 0.05). No association of MSI was found between the patients’ age and gender or with the size and histopathological grade of the tumors.

Key words: Microsatellite  instability (MSI), hered­itary nonpolyposis colorectal cancer (HNPCC), colorectal cancers (CRC), BAT26